The present invention relates to pharmaceutically useful indolin-2-one derivatives or their salts, and to chondrogenesis promoters, cartilage repair agents and cartilage diagnostic reagents containing the indolin-2-one derivatives or their pharmaceutically acceptable salts.
Cartilage in the body generally consists of chondrocytes and fibrocytes, which are specialized connective tissue cells, and an amorphous gel-like matrix in which they are embedded, and it forms a part of the supportive tissue of the body.
In warm-blooded animals including humans, cartilage forms the skeleton, joints, tracheae, auricula, nose and the like. That is, it performs a central role in functions that are indispensable to the survival of warm-blooded animals, including acting as a template for bone during growth (growth cartilage), and contributing to smooth joint movement (articular cartilage), respiration (tracheal cartilage, nasal cartilage) and hearing (auricular cartilage). Thus, degeneration or destruction of these types of cartilage causes various degrees of detriment to the body depending on the site and severity of degeneration or destruction.
For example, among the aforementioned functions in which cartilage plays a role (growth, joints, respiration, hearing, etc.), the smooth movement of joints is particularly impaired by degeneration or destruction of articular cartilage in such conditions as chronic rheumatoid arthritis or osteoarthritis. Degeneration or destruction of articular cartilage is believed to be the major cause of the walking difficulty that results from such diseases.
The prospect of suppressing articular degeneration or destruction or of promoting chondrogenesis has been raised as a possible method of treating conditions such as chronic rheumatoid arthritis and osteoarthritis (J. Rheum. 22(1), Suppl. 43:136-139, 1995, Lab. Invest. 78(2):133-142).
Several different organism-derived substances and low molecular substances are known to have effects of promoting chondrogenesis or of inducing proliferation of chondrocytes. Substances that have been reported to have chondrogenesis-promoting effects include growth factors such as TGF-xcex2 (Transforming growth factor xcex2), BMP-2 (J. Bone Joint Surg. 79-A(10):1452-1463, 1997), concanavalin A which is a type of lectin (J. Biol. Chem., 265:10125-10131, 1990) and osteogenin (BMP-7), as well as low molecular substances such as vitamin D derivatives (1xcex1, 25-D3) (Cancer Res., 49:5435-5442, 1989), vitamin A derivatives (retinoic acid) (Dev. Biol., 130:767-773, 1988), vanadates (J. Cell Biol., 104:311-319, 1987), benzamides (J. Embryol. Exp. Morphol., 85:163-175, 1985), benzyl xcex2-D-xyloside (Biochem. J., 224:977-988, 1984), triiodothyronines (T3) (Endocrinology, 111:462-468, 1982), prostaglandin derivatives (PGE2, U44069) (Prostaglandin, 19:391-406, 1980), dbcAMP (J. Cell. Physiol., 100:63-76, 1979) and 8-Br-cAMP(J. Cell. Physiol., 100:63-76, 1979).
Of these organism-derived substances and low molecular substances, TGF-xcex2 holds the most promise as a useful treatment agent, and TGF-xcex21, which is one isoform of TGF-xcex2, has been reported to promote chondrogenesis when intraarticularly administered (Lab. Invest. 71(2):279-290, 1994). Also, since TGF-xcex21 suppresses arthritis-induced loss of proteoglycans in articular cartilage, or stated differently, it inhibits destruction of articular cartilage due to its anabolic effect on articular cartilage when administered intraarticularly in experimental animal models with induced arthritis, its possibility as a useful treatment agent for articular disease such as rheumatism has been suggested (Lab. Invest. 78(2):133-142, 1998).
However, even TGF-xcex2 which holds the most promise as a useful treatment agent has been reported to provoke synovitis even while promoting chondrogenesis, and this therefore poses a serious problem for its use as a treatment agent for articular diseases (Lab. Invest. 71(2):279-290, 1994), for which reason it has not been applied in the clinic as a treatment agent for such conditions. In summary, then, no practical treatment agent therapy exists that is based on promoting chondrogenesis.
It is an object of the present invention to overcome the aforementioned drawbacks of the prior art by providing a chondrogenesis promoter and cartilage repair agent that are able to promote chondrogenesis or induce proliferation of chondrocytes.
It is another object of the invention to provide a reagent with chondrogenesis promoting action which is useful for biological, physical or chemical research on cartilage.
It is yet another object of the invention to provide indolin-2-one derivatives that are useful as chondrogenesis promoters.
It is still yet another object of the invention to provide indolin-2-one derivatives that are useful as bone fracture repair promoters.
As a result of diligent research aimed at achieving these objects, the present inventors have completed the present invention upon the discovery that indolin-2-one derivatives having a specific structure exhibit a chondrogenesis promoting effect.
In other words, a chondrogenesis promoter according to the invention comprises as an active ingredient a compound represented by general formula (I) or a salt thereof: 
wherein
R1 represents a halogen atom, a lower alkyl group, a lower alkoxy group, a hydroxyl group, a nitro group, a trifluoromethyl group, a lower alkylthio group, an acyl group, a carboxyl group, a mercapto group or an amino group with an optional substituent;
R2 represents a hydrogen atom, a lower alkyl group with an optional substituent, a lower alkenyl group with an optional substituent, a lower alkynyl group with an optional substituent, a lower alkoxy group with an optional substituent, an acyl group with an optional substituent, an aryl group with an optional substituent or a heterocyclic group with an optional substituent;
R3 represents a lower alkyl group with an optional substituent, a cycloalkyl group with an optional substituent, an aryl group with an optional substituent or a heterocyclic group with an optional substituent;
R4 represents a hydrogen atom, a lower alkyl group with an optional substituent, an aryl group with an optional substituent, a heterocyclic group with an optional substituent, xe2x80x94OR5, xe2x80x94SR5 or xe2x80x94NR6R7 wherein R5, R6 and R7 may be the same or different and each represents a hydrogen atom, a lower alkyl group with an optional substituent, a cycloalkyl group with an optional substituent, an aryl group with an optional substituent, a heterocyclic group with an optional substituent, a lower alkoxy group or an amino group with an optional substituent, and R6 and R7 may together form a group represented by xe2x80x94(CH2)mxe2x80x94 or xe2x80x94(CH2)lNR8(CH2)kxe2x80x94 wherein k, l and m each represent an integer of 1-8 and R8 represents a hydrogen atom or a lower alkyl group;
X and Y may be the same or different and each represents xe2x80x94CH2xe2x80x94, xe2x80x94NHxe2x80x94 or xe2x80x94Oxe2x80x94, and n represents an integer of 0-4.
A cartilage repair agent according to the invention also comprises as an active ingredient a compound represented by general formula (I) above or a salt thereof.
A reagent for biological, physical or chemical research on cartilage according to the invention also comprises as an active ingredient a compound represented by general formula (I) above or a salt thereof.
An indolin-2-one derivative according to the invention is represented by the following general formula (IV): 
wherein R12 represents a lower alkyl group substituted at the same carbon with two lower alkoxy groups which is optionally substituted with 1-5 halogen atoms.
Also, R12 of the indolin-2-one derivative according to the invention may be represented by general formula (V): 
wherein R13 and R14 may be the same or different, and each represents a lower alkyl group which is optionally substituted with 1-5 halogen atoms.